This invention relates to a two-piece master track link for joining together the ends of an endless track as used in bulldozers, track-laying tractors and other heavy-duty track vehicles.
An endless track for tractors is usually formed by a plurality of shoes fixed by bolts to links which in turn are mutually and rotatably connected by means of pins and bushings.
It is conventional to provide a coupling pin or a junction link in each endless track. This piece, which is firmly retained in position during the operating condition, allows the removal of the track from the vehicle.
As a general rule (for removing the endless track, particularly during the work on field) a junction link formed by several parts is more practical and easy to handle than the coupling pin, particularly in respect to heavy duty machines.
Moreover, it is required to use a hydraulically actuated tool or a manually actuated hammer for assemblying and disassemblying the endless track at the field of work, thereby rendering the assembly and disassembly of the endless track troublesome and difficult. Further, if the master pin due its tolerances is loosened too much, the master pin tends to be drawn out of the mating portion of the endless track, which may result in damage of the endless track.
For this reason, junction links have been developed, formed of two or more parts, which are connected to one another by lag screws which fasten also the shoe, and are joined by multiple coupling profiles located on a more or less wide zone of the separation line of said parts, either by single tooth interlocking coupling profiles, or by means of connection pins forced in the two parts parallelly to the axis of the locking screws, or by special specific connection shoes.
There are already known several kinds of two-piece master track links. For example, the U.S. Pat. No. 3,427,079 discloses a two-piece master track link including two parts having mating surfaces defining multiple mating serrations arranged generally parallel with the bores in the parts. The link parts interlock at their serrated juncture to form a continuous central link mass for resisting tensile forces exerted on the end portions of the link parts.
It should be pointed out that the central juncture portion of this track link is disposed on the diagonal plane and has a plurality of interlocking serrations. Such a structure is difficult and costly to manufacture, and close tolerances are required to assure optimum coupling of the interlocking surfaces and alignment of the shoe bolts utilized to secure the track shoe to the link part.
The U.S. Pat. No. 4,105,260 also discloses a track link composed of two parts in which joining surfaces are formed with a plurality of mating serrations. Keytype means are provided to reduce or eliminate the shear loads between the track shoe and the link, however without avoiding the above mentioned drawbacks of the plurality of interlocking serrations.
The German patent application No. 1,400,481 discloses a structure of the track link in which the contacting surfaces of the half-links are provided with one or more substantially vertical projections on the central horizontal face of the mating surface of at least one half-link, which projections engage the corresponding recesses on the mating surface of the other half-link.
Obviously, such projections are not adapted for high stresses occuring in the heavy-duty track vehicles.
The U.S. Pat. No. 3,096,661 discloses a two-piece master track link including a notch and a profiled coupling key. The conformation of the profiled key with the notch and thus the junction features of this track link structure can not be adapted for the heavy-duty track vehicles, since only a side wall of that notch and profiled key sustains the stresses exerted on the link.
The U.S. Pat. No. 4,050,750 shows a two-piece master track link which, however, requires a third separate piece for coupling two half-links to one another at their central horizontal mating surface.
This third piece, necessary for coupling the two half-links with one another, provides for its function by a less or more forced coupling, thus rendering uneasy and difficultous the operation of joining and disjoining the master track link.
The German patent application DE No. 30 21 325 discloses a two piece master track link having a coupling surface with a single tooth and a respective recess, said tooth having a small hight which is reduced to a value just necessary for withstanding the traction stress of the chain in the working condition, said tooth being inclined so as to assume an almost orthogonal posittion with respect to the traction force of the chain when this last is wound on the vehicle wheel (about 30.degree.).
Moreover, the central contact zone is arranged in the master link assembly in the symmetrical position with respect both to the pin bore-bushing bore axis and vertical plane parallel to the axes of said bores and passing through the intersection point of said axis and the central contact zone, so that there is wholly missing a balancing of the elastic deformations of the two half-link parts coupled with one another, which parts have a stiffness different therebetween owing to the different transverse size of said half link parts and thus of their weight.
The height of the inclined central contact surface is limited and causes thus a further increase of the stiffness of the master link.
Furthermore, this master link does not offer a sufficient safety against casual opening thereof when the bolts are not yet inserted or are removed during the joining or disjoining operation owing to both said limited height of the central contact surface and an inclination of about 25.degree.-30.degree. of said surface with respect to the vertical plane. Finally, this remarkable inclination causes a considerable part of the traction force of the chain exerted during the work to act onto the connection bolts and since, moreover, said force is variable in dependance on the working conditions and has also a pulsating behaviour, it causes overcharges and possible ruptures of the bolts.
Summarizing, all the known two-piece master track links have the drawback consisting in that the bolts tend to loose and unscrew after a certain time owing to a low elasticity degree of the master link and also in that the coupling surfaces of the two half-links require a high machining precision which increases the production costs, without solving the problem of rendering more easy the joining and disjoining operation of the master track and reducing the forces acting onto the screws and deriving from the working stresses exterted by the chain, which forces may overcharge the screws and cause the rupture thereof.